Soil Population 335 



Soil Population as a Whole 



The numerous interrelationships existing in the soil between plants 

 and microorganisms, on the one hand, and between soils and micro- 

 organisms, on the other, demonstrate the manifold activities of the 

 extensive microbiological population inhabiting the soil. These 

 microorganisms are responsible for numerous chemical reactions 

 taking place in the soil. The organisms do not exist and multiply 

 in the soil in a fixed manner. Their growth and activities are con- 

 stantly modified, depending upon the nature of the soil, its treat- 

 ment, the crop grown, and various changes in environmental condi- 

 tions. The microbiological population of any soil, at a given mo- 

 ment, ma\- be in a state of equilibrium. Any modification of this 

 equilibrium will bring about a marked change, both in qualitative 

 composition and in quantitative interrelations, among the constituent 

 members of this population. 



Under natural conditions, modifications of this equilibrium take 

 place constanth'. The freezing of soil in winter, the melting of 

 snow and the thawing of ice in spring, the frequent wetting and dry- 

 ing of soil in summer and in fall, the addition of leaves, roots, and 

 other plant stubble from the growing vegetation, will continuously 

 modify the soil population by changing the conditions of the soil. 

 The nature of the crop and the treatment of the soil, especially culti- 

 \'ation and fertilization, further influence in many ways the nature 

 and composition of the soil microbiological population. 



Aside from those modifications, man has learned to influence the 

 soil population through various specific treatments, such as addition 

 of lime or of acid-reacting fertilizers, air-drying or steam-steriliza- 

 tion, or treatment with various antiseptics. This is true particularly 

 of greenhouse soils and of nursery beds. All these treatments bring 

 about marked changes in the composition of the microbiological 

 population. 



Selected Bibliography 



1. Ensminger, L. E., and Gieseking, J. E., Resistance of clay-adsorbed pro- 

 teins to proteolytic hydrolysis, Soil Sci., 53:205-209, 1942. 



2. Geltser, F. Y., Influence of the type of organic matter on soil structure, 

 Trans. Sov. Sect. Intern. Soc. Soil Sci., 5:115-120, 1936. 



